1. Field of the Invention
The present invention relates to a numerical controller, and particularly relates to a numerical controller that performs skiving machining control.
2. Description of the Related Art
Skiving machining refers to a machining method of cutting a workpiece by sending a cutting tool in a tangential direction of the workpiece when the workpiece is cut using the cutting tool (Japanese Industrial Standard (JIS) B0106 0.209). In skiving machining in a turning machine, a workpiece is machined while a Y axis moves using a tool having a straight blade obliquely arranged with respect to a rotation axis of a rotating work (for example, JP 3984052 B2).
When such skiving machining is performed by a conventional numerical controller, movement of a Y axis needs to be commanded in accordance with movement of a Z axis. FIG. 7 is a diagram illustrating a cutting path of cutting work with respect to a workpiece when skiving machining is performed and a movement path of a tool when cutting work is performed along the cutting path. As illustrated in FIG. 7, in the skiving machining, the cutting path of the cutting work with respect to the workpiece is in a direction of a rotation axis (Z axis direction), whereas cutting is performed by moving the tool in a direction in which the straight blade is directed (approximately vertical direction of the straight blade), and thus a tool path corresponds to a direction of a synthetic vector of the Z axis direction and a Y axis direction inclined with respect to the rotation axis direction.
Conventionally, at the time of preparing a skiving machining program, an operator has calculated a Z axis and Y axis movement amount of a tool path commanded by the program such that a cutting path corresponds to the path illustrated in FIG. 7, and prepared the program based on a result of calculation. However, this operation is a heavy burden for the operator. For this reason, it is desired that a numerical controller automatically calculate a tool path when the operator commands the cutting path of skiving machining by the program.
FIG. 8 is a diagram illustrating a relation between a movement amount Zc and a feed speed Fc of a cutting point, and each value related to movement of the tool. Further, FIG. 9 is a diagram illustrating each value related to a blade edge of the tool. When the movement amount of the tool in the Z axis direction is set to Za, the movement amount of the tool in the Y axis direction is set to Ya, and a synthetic feed speed of the tool in the Z axis direction and the Y axis direction is set to Fa at the time of moving the tool such that the movement amount of the cutting point becomes Zc and the feed speed of the cutting point becomes Fc as illustrated in FIG. 8, an effective blade edge length of the tool is set to Lv, and a tool angle is set to θ, a relation to each value can be expressed by the following Equation 1. In this way, the numerical controller can automatically calculate the tool path based on a command of the cutting path in skiving machining using Equation 1.
                    ⁢          [              Equation        ⁢                                  ⁢        1            ]                                    Movement          ⁢                                          ⁢          amount          ⁢                                          ⁢          of          ⁢                                          ⁢          tool          ⁢                                                            ⁢                                                          ⁢          in          ⁢                                          ⁢          Y          ⁢                                          ⁢          axis                                      Ya          =                      Lv            ×            sin            ⁢                                                  ⁢            θ                                              direction                                                                            Movement          ⁢                                          ⁢          amount          ⁢                                          ⁢          of          ⁢                                          ⁢          cutting          ⁢                                          ⁢          point          ⁢                                          ⁢          in          ⁢                                          ⁢          Z                                      Zy          =                      Lv            ×            cos            ⁢                                                  ⁢            θ                                                        axis          ⁢                                          ⁢          direction          ⁢                                          ⁢          in          ⁢                                          ⁢          association          ⁢                                          ⁢          with          ⁢                                          ⁢          movement                                                                                    of          ⁢                                          ⁢          tool          ⁢                                          ⁢          in          ⁢                                          ⁢          Y          ⁢                                          ⁢          axis          ⁢                                          ⁢          direction                                                                                    Movement          ⁢                                          ⁢          amount          ⁢                                          ⁢          of          ⁢                                          ⁢          tool          ⁢                                          ⁢          in                                      Za          =                      Zc            -            Zy                                                        Z          ⁢                                          ⁢          axis          ⁢                                          ⁢          direction                                                                                    Feed          ⁢                                          ⁢          speed          ⁢                                          ⁢          of          ⁢                                          ⁢          tool          ⁢                                          ⁢          in          ⁢                                          ⁢          Z          ⁢                                          ⁢          axis          ⁢                                          ⁢          direction                                      Fz          =                      Fc            -                                          (                                  Zy                  /                  Zc                                )                            ×              Fc                                                                    Feed          ⁢                                          ⁢          speed          ⁢                                          ⁢          of          ⁢                                          ⁢          tool          ⁢                                          ⁢          in          ⁢                                          ⁢          Y          ⁢                                          ⁢          axis          ⁢                                          ⁢          direction                                      Fy          =                                    (                              Zy                /                Zc                            )                        ×            Fc            ×            tan            ⁢                                                  ⁢            θ                                                        Synthetic          ⁢                                          ⁢          feed          ⁢                                          ⁢          speed          ⁢                                          ⁢          of          ⁢                                          ⁢          tool                                      Fa          =                                                    Fz                2                            +                              Fy                2                                                        
FIG. 10 is a diagram illustrating an example of automatically calculating a tool path based on a command of a cutting path of taper machining by skiving machining when the cutting path is commanded using the above Equation 1. As illustrated in FIG. 10, in the case of performing taper machining by skiving machining, when the movement amounts Zc and Xc of the cutting point and the feed speed Fc are commanded by the program, movement amounts in an X axis direction, the Y axis direction and the Z axis direction and the feed speed are properly corrected, and thus it is possible to obtain a machined shape as programmed.
FIG. 11 is a diagram illustrating an example of automatically calculating a tool path based on a command of a cutting path of circular arc shape machining by skiving machining when the cutting path is commanded using the above Equation 1. As illustrated in FIG. 11, in the case of commanding circular arc shape machining by skiving machining, even when movement amounts in the X axis direction, the Y axis direction and the Z axis direction and a feed speed are corrected in advance using the above Equation 1 to perform circular arc interpolation on the tool path, there is a problem that the cutting path becomes a distorted circular arc shape.